The Annals of Ulster record that in March 804 the coastal area of West Clare around Milltown Malbay was struck by what appears to have been a tsunami. Over a thousand people were killed. Mutton Island, the largest island off the coast of Clare and then called Fitha, was split into three islands that are now called Mutton, Inismattle and Roanshee.
The Annals of Ulster record: Violent thunder, accompanied by wind and fire, on the night before St. Patrick's Day, which destroyed many persons, i.e. one thousand and ten in Corcu Baiscinn; and the sea divided the island of Fita into three parts, and covered the land of Fita with sand, that is as much land as would support 12 cows.
The large number of people killed, the splitting of Mutton Island and the large amount of sand washed-up on the shore suggest that this event may have been a tsunami that inundated the coastal area of Clare.
The Irish annals are a unique collection of annual records made in the monasteries of Ireland of political, cultural, social, religious, climatic events and disasters that took place in Ireland between sixth and sixteenth centuries.